The present invention relates to an optical pickup for optically reproducing recorded information from an information storage medium or optically recording information in an information storage medium, and more particularly to an optical pickup for reproducing information recorded on an optical disk in a compact disk (CD) player, a laser vision disk (LVD) player, or the like.
Heretofore, optical pickups of the type described above are made up of many discrete components including a semiconductor laser, a polarizing prism, a condensing lens, a photodetector, etc.. It has been difficult to adjust the positions of these individual components relative too each other.
Various optical pickups which include components, except an object lens, mounted on a single semiconductor substrate have been developed. One such optical pickup is disclosed in Japanese Laid-Open Patent Publication No. 64(1989)-33734. The disclosed optical pickup comprises a semiconductor substrate, a semiconductor laser mounted on the semiconductor substrate for emitting a laser beam to read recorded information, a beam splitter mounted on the semiconductor substrate for reflecting the laser beam toward an optical disk and dividing a laser beam reflected from the optical disk into two laser beams through a plurality of reflections, and first and second photodetectors mounted on the semiconductor substrate for detecting the intensities of the two reflected laser beams from the beam splitter. Based on the laser beam intensities detected by the first and second photodetectors, the presence and absence of pits or holes in the recording surface of the optical disk are converted into an electric RF signal for reproducing the information recorded in the optical disk.
In order to divide the laser beam reflected from the optical disk into the two laser beams, the reflected laser beam has to be reflected a plurality of times by the beam splitter. Because of this requirement, a plurality of facets of the beam splitter need to be ground into smooth surfaces. In addition, a dielectric multilayer film is evaporated on one of the ground facets to provide a semireflecting mirror surface thereon, and a reflective film is deposited on the other ground facet. Therefore, the conventional optical pickup suffers a first problem in that a complex process is required to fabricate the beam splitter, and the optical pickup is relatively large in size.
Furthermore, it is necessary to produce the beam splitter separately from the semiconductor substrate. Since it is difficult to manufacture the beam splitter with precision, the prior optical pickup has a second problem in that the beam splitter cannot be reduced in size, and hence the size of the overall optical pickup remains relatively large in size. Moreover, the beam splitter has to be subsequently mounted on the semiconductor substrate with high accuracy, resulting in a third problem as to a yield reduction. A fourth problem of the conventional optical pickup is that the junction between the semiconductor and the beam splitter mounted thereon causes a loss of optical energy.